This invention relates to seals for sealing the annulus between a tubing hanger assembly and a casing hanger assembly and more particularly to a nose seal on the lower end of the tubing hanger assembly for sealingly engaging the previously run casing hanger assembly.
The subsea exploration and production of oil and gas reserves includes suspending from a wellhead housing a plurality of concentric strings of casing and tubing within the bore of the well. A series of casing hangers, each suspending a casing string, are stacked and supported within the wellhead housing. In the installation of successive casing strings within the well, a casing hanger assembly suspending a casing string is lowered through the bop stack for suspension within the wellhead housing. After the successive strings of casing are installed and cemented into the well, a tubing hanger assembly suspending one or more strings of tubing is lowered into the wellhead housing and suspended within the last installed casing hanger assembly.
Tubing hanger assemblies designed for subsea wellheads require that a seal be established between the last casing string and the tubing string. This seal seals the annulus between the casing and tubing strings and is often located near the lower end of the tubing hanger assembly for sealing with the previously run casing hanger assembly. This type of seal is referred to as a nose seal.
Tubing hanger assemblies may also include a seal located near the upper end of the tubing hanger assembly for sealing with the internal diameter of the wellhead housing. This seal assembly is either identical to or substantially the same as the seal assemblies used to seal the annulus between previously run casing hanger assemblies.
Some prior art tubing hanger assemblies include both a nose seal for sealing between the tubing hanger assembly and previously run casing hanger assembly as well as an upper seal for sealing between the tubing hanger assembly and the wellhead housing. Such prior art tubing hanger assemblies thus have both a nose seal and a regular casing hanger seal assembly.
In the above prior art sealing arrangements, the great majority of the seals are resilient seals and the remainder are combination metal and elastomer seals. In either case, the seal between the seal assembly and the tubing hanger body and the seal between the seal assembly and the casing hanger and/or wellhead housing are both made downhole.
The present invention overcomes the deficiencies of these prior art tubing hanger seals.